1. Field of the Invention
The present invention relates to a vibration wave motor, and more particularly to the structure of a member which frictionally contacts a vibration member of the vibration wave motor.
2. Related Background Art
A vibration wave motor disclosed in U.S. Pat. No. 4,513,219 has an electro-mechanical energy, such as an electrostrictive element, arranged on a vibration member. A periodic voltage is applied to the element to develop a travelling vibration wave, and the vibration member is press-contacted to a movable member to move the movable member by the vibration wave. In such a vibration wave motor, if a torque transmission efficiency between the vibration member of the motor and the member which frictionally contacts the vibration member is not sufficiently high, the energy efficiency of the vibration wave motor is lowered.
Several methods for improving the torque transmission characteristic between the vibration member and the member which frictionally contacts the vibration member have been proposed. One of the reasons why the torque transmission efficiency is not sufficiently high is that the vibration member and the contact surface of the member which frictionally contacts the vibration member are not sufficiently parallel and an apex of the vibration generated in the vibration member does not uniformly contact the member when viewed microscopically and hence the torque is not well transmitted. As an approach to resolve the above problem, Japanese Unexamined Patent Publication No. 188381/1984 discloses a method in which the member which frictionally contacts the vibration member is supported by an elastic member, such as rubber, so that the member is movable with a certain freedom and the vibration generated in the vibration member is transmitted efficiently to the member.
Japanese Patent Application Laid-open No. 272358/1984 (assigned to the assignee of the present application) discloses a method in which a rotor which contacts the vibration member is of a flange shape having a flange inclined outwardly of a center of rotation and good contact between the vibration member and the rotor is maintained by elastic deformation of the flange.
A rotated flange type ring-shaped rotor is shown in FIGS. 1A and 1B.
FIG. 1A shows a sectional view of the flange type rotor and FIG. 1B is an enlarged sectional view of the flange shown in FIG. 1A. Numeral 1 denotes the flange type rotor having the flange, and numeral 2 denotes a vibration member for frictionally driving the rotor 1. The rotor 1 is frictionally driven by longitudinal vibration generated in the vibration member 2 and the flange of the rotor 1 is elastically deformed as shown by broken lines in FIG. 1B in accordance with the longitudinal vibration because of the elasticity of the flange. The elastic deformation results in a locus 3 shown by a chain line of the flange which slightly expands outward when the flange is elastically deformed as shown by the broken line.
Since the vibration member 2 is ring shaped, the vibration generated in the vibration member 2 includes not only the longitudinal vibration but also a vibrating torsional component as shown by broken lines in FIG. 2. The locus of the vertical vibration generated by the vibration member 2 is slightly inclined inward by the torsional component, as shown by a solid line 4 in FIG. 2. In FIGS. 1B and 2, chain lines 6 show center lines of the ring surface of the ring-shaped vibration member.
Accordingly, in the prior art flange type rotor, the locus of movement of the flange of the rotor does not coincide with the locus of movement of the vibration member by the vibration, and they frictionally contact each other at the contact areas with some slippage therebetween. This slippage is not effectively used as a drive force but it is a loss which prevents the improvement of efficiency.
In the vibration wave motor of a type other than the vibration wave motor having the flange type rotor, if the locus of vibration of the vibration member does not coincide with the locus of displacement of the contact area of the member which frictionally contacts the vibration member, a loss due to a slippage is a serious problem in improving efficiency, as is the case for the flange type rotor.